Civil Engineering Reference
In-Depth Information
had to be considered in the analysis. The elastic-plastic formulation is able to simulate more realistic
material-flow and, hence, to produce more accurate deformation and stress results. The method, however,
requires more complex numerical treatment.
Early applications of FE in metal forming were mainly for the simulation of the sequence of die-filling
and the computation of tool-stresses; to enable this, the forming process and work-material property
was somewhat simplified. Due to the theoretical breakthrough in plastic formulations and numerical
solution methods, rate-dependence and temperature effects could be incorporated into analyses as well
as the solution of thermally-coupled problems. FE simulation is currently capable of being applied to
warm and hot forming processes [38, 39]. The dynamic characteristics of forming-processes have now
been evaluated, particularly since the advent of “EXPLICIT” FE methods. Success in the application of
FE simulation for analyzing metal forming was also due to the significant progress which had been made
in numerical modeling of contact and friction problems [40], such as large sliding 3D contact problems
[41]. The feasibility and robustness of simulation of material sliding along the tool-surfaces is essential
for the simulation of large-deformation forming processes.
Early development in the applications of FE for analyzing metal forming focused on small-scale
software which was usually programmed for a particular forming process or a specific component-form.
These are gradually being replaced by the development of large-scale, commercial plastic-analysis soft-
ware, such as ABAQUS, MARC, Forge3, and DEFORM. The application of this software was further
promoted by the availability of efficient pre- and post-processing software, such as PATRAN, SDRC I-deas,
and ABACAE. More recently, adaptive and automatic remeshing techniques have been added to some
software (e.g. MARC, DEFORM, and Forge3), which added further flexibility and efficiency to FE simu-
lation of metal-forming processes. Taking FE software as a neutral engine, some CAD/CAM or CAE systems
are being built [42] with built-in artificial intelligent techniques for the development of Knowledge-based
Systems for design of forming operations [43-45].
Currently, FE simulation is being applied to various fields of analysis and design of metal forming.
These may be summarized as follows:
General flow simulation and deformation analysis
—The bulk flow of work-material may be simulated
using FE to analyze the property of deformed material, e.g., stress-strain condition in the work-material,
and to determine forming force requirement and pressure contour on the tool-surface. The simulation
has been applied to the analysis of various bulk-metal forming processes: upsetting, extrusion, open-
and closed-die forging, and shape rolling. Current efforts in developing FE approaches concentrate on
the analyses of more complex process conditions or the forming of new materials. FE is also widely used
to analyze sheet deformation in bending, blanking, stamping, and deep drawing. EXPLICIT FE methods
are particularly efficient for these applications. FE is often used to simulate the spring-back, wrinkling,
and fracturing of the sheet.
A forming process may be optimized using FE analysis with reference to the
product-quality. This may be achieved by the prediction of the development of work-material flaws, e.g.,
flow imperfections (buckling, folding, underfilling) and the fracture of material. For the latter, the criteria
of ductile fracture of work-material is usually incorporated into FE analysis to predict fracture. Process
parameters, preform geometry, and forming sequence may be designed to enable “optimal” pattern of
material flow or “optimal” state of stresses and strains in work-material, with a view to preventing the
development of the flaws. Forward simulations with trials or backward tracing simulation may be used
to achieve these. The optimization algorithm may also be incorporated into FE formulation to establish
“automatic” FE-optimization procedures, such as penalty finite element methods and shape optimization
methods. These methods are currently limited to the analysis of simple forming operations. Further effort
is required to improve the efficiency of the methods.
Friction plays an important rule in prescribing the quality of product. A variety of friction models
are currently available, each of these being limited to a particular range of pressure, temperature, and
type of interfacial material. Friction models may be chosen with reference to the accuracy of FE results
and the numerical stability of contact analysis. FE formulation also provides efficient means for friction
design by which complex descriptions of friction can be efficiently incorporated into the FE model.
Product-quality control
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